The invention relates to regenerative turbine pumps which in some cases are also referred to as turbine pumps, periphery pumps, turbulence pumps, or friction pumps. The turbine pump name has been used because of the plurality of vanes, resembling those of a steam turbine, that are machined into the periphery of the impeller that is rotated at high speed. Two basic types are known. One type has inclined vanes on only one side of an impeller. The more commonly used type has radial vane impellers. While the invention will be described in terms of the latter type it will be understood by those skilled in the art that the invention has application to both forms.
Regenerative turbine pumps are particularly suitable for air conditioning, refrigeration, and heating applications. Regenerative turbine pumps will move a relatively low flow of fluid at a relatively high head. More specifically, such pumps have a relatively steep head capacity curve. The regenerative turbine pump has higher efficiencies at low flows than a centrifugal pump. A regenerative turbine type pump typically will produce several times the pressure produced by a centrifugal pump having an impeller of equal diameter and operating at the same speed.
Conventional regenerative turbine pumps utilize close running tolerances. More particularly, the impeller vanes usually run at very close axial clearances within machined channel rings disposed within the pump housing to minimize recirculation losses. The channel ring around each impeller provides a circular channel around the vane area of the impeller from the inlet to the outlet. It is known in the prior art to provide greater axial clearance between the vanes and the adjacent channel ring wall near the inlet of the pump than at parts of the channel ring. It is also known in the prior art to gradually decrease that axial clearance between the sides of the vanes and the side walls of the channel ring from a point near the inlet through an angular sector.
In a single stage regenerative turbine pump the fluid enters the channel on both sides of the impeller adjacent to a first circumferential part of the impeller. The vanes carry the fluid within the channel for almost a full revolution. A blocker or splitter directs the fluid through an outlet.
Some forms of regenerative turbine pumps may be multistage structures. Two stage regenerative turbine pumps direct a fluid from a first stage to a second stage. If the respective discharges are offset by 180 degrees the radial loads on the bearings are nearly balanced and shaft deflection is minimized.
Pumps of this type having a top center line discharge are self venting and have the ability to handle vapors without vapor lock. This characteristic allows handling of boiling liquids and liquified gases at suction heads slightly over the vapor pressure.
Regenerative turbine pumps have many advantages including even a characteristic of superior suction lift. More particularly, they are preferred for lifting liquids from lower levels and particularly for hot liquids and liquids that vaporize at normal temperatures.
Although regenerative turbine pumps are desirable for superior suction lift there are still many applications where there is insufficient net positive suction head to operate conventional regenerative turbine pumps. Net positive suction head is the absolute pressure, above the vapor pressure of the liquid being pumped, at the pump suction flange.
If the net positive suction head pressure available to the pump is insufficient, the pump will cavitate and serious operational difficulties may develop. These troubles can include reduction in capacity and efficiency, excessive vibration, reduced life of pump parts due to cavitation erosion, and damage to the pump from possible vapor lock and running dry.
One way to solve the problem is to set up the pumping system so that the NPSH (net positive suction head pressure) available from the system is greater than the NPSH required by the pump. In some pump systems this has been achieved by an elevated inlet tank or other costly design considerations. For example, it may be necessary to lower the pump with respect to a supply tank by providing a pit in which the pump is disposed. For other installations multiple pumps in parallel or a discrete booster pump in series or large pipelines to decrease friction losses. Discrete rotating impellers have also been used in series with another impeller to overcome the pressure drop between the suction flange of the pump and the entrance to the impeller vanes.
The change of the physical arrangement is often inconvenient, expensive or even impossible. Therefore, when a pump is selected for a particular application the NPSH requirement of the pump is an important characteristic.
It is an object of the invention to provide a construction that will have a lower net positive suction head pressure requirement.
It is an object of the invention to provide apparatus that will have a longer service life because of the elimination of operating problems such as cavitation.
It is an object of the invention to provide apparatus which is inexpensive to manufacture.
Still another object of the invention is to provide apparatus that will not increase the assembly time in any way.